As a magneto-resistive effect device having an electrical resistance that varies depending on a magnetic field, a TMR device (also referred to as an MTJ device) that utilizes a Tunnel Magneto Resistance (TMR) effect to store information or detect magnetism is known. In recent years, MTJ devices are expected to be used for a Magnetic Random Access Memory (MRAM) or the like.
Patent Literature 1 discloses an MTJ device and a manufacturing method thereof. The MTJ device includes the structure in which a free layer (free magnetized layer), a tunnel barrier layer, and a reference layer (fixed magnetized layer) are stacked, and the magnetized directions of the free layer and the reference layer are in parallel to the stack direction, respectively.
In order to improve the characteristics of an MRAM device using an MTJ device, it is important to increase the magneto-resistive ratio (MR ratio). It is known that the stack structure of CoFeB/MgO/CoFeB disclosed in Patent Literature 1 exhibits a high MR ratio greater than 100%.
The MTJ device using a technology disclosed in Patent Literature 1 is an MTJ device having the bottom spin structure. The MTJ device of Patent Literature 1 has a CoFeB layer as a reference layer (fixed magnetized layer), a CoFeB layer as a free layer (free magnetized layer), and an MgO layer as a tunnel barrier layer interposed between the reference layer and the free layer. The MgO layer (tunnel barrier layer) is formed by forming an Mg film and oxidizing the Mg film. Further, in order to prevent diffusion of oxygen from the MgO layer to the free layer, an Mg layer is further formed on the MgO layer on the free layer (free magnetized layer) side of the MgO layer. The Mg layer formed on the free layer (free magnetized layer) side of the MgO layer is referred to as an Mg cap.